Reliability Analysis of Rainwater Harvesting in Three Texas Cities
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Population growth and a prolonged drought have raised concerns about the sustainability of water resources in Texas. Recent state legislation has made financial assistance available towards the development of water supplies. The purpose of this study is to inform decision makers at state and local levels, as well as property owners about the amount of water that can be supplied by rainwater harvesting systems in Texas so that it may be included in any future planning. Reliability of a rainwater tank is important because people want to know to what degree a source of water can be depended on. Performance analyses were conducted on 3 cities under different climate conditions and multiple scenarios to demonstrate the importance of optimizing rainwater tank design. This was accomplished using a daily water balance model and running simulations on a range of tank sizes appropriate for rainwater harvesting at the household level. Reliability curves were produced and reflect the percentage of days in a year that water can be supplied by a tank. Operational thresholds were reached in all scenarios and mark the point at which reliability increases by only 2% or less with an increase in tank size. Maximum thresholds were also reached in some scenarios and indicate a tank size that provides the maximum achievable reliability. Additional simulations considered several average years of rainfall for each city under a single scenario to determine an average optimal tank size. A payback period analysis was conducted on these tank sizes to estimate the amount of time it would take to recoup the cost of installing a rainwater harvesting system.